Error:conversion from 'double' to 'int', possible loss of data

[DesmondLee]

There is an error conversion:
Error message :

warning C4244: '=' : conversion from 'double' to 'int', possible loss of data
warning C4244: '+=' : conversion from 'double' to 'int', possible loss of data
warning C4244: '=' : conversion from 'double' to 'int', possible loss of data
warning C4244: '+=' : conversion from 'double' to 'int', possible loss of

  #include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main()
{
	double a[10];
    int i;
	double const gravity=9.807;
	double const PI = 3.1415927;
	double dev=0,f4=0;
	double f1=2*PI;
	double f2,f3;

	cout<<"Enter the period measured for the following pendulum lengths:"<<endl;
	for(i=2.50; i<=4.75; i+=0.25)
	{
		cout<<fixed<<setprecision(2)<<i<<" m : " ;
		cin>>a[i];
	}
	cout<<left<<setw(10)<<"Length(m)"<<left<<setw(20)<<"Calculated Period(s) "<<left<<setw(20)<<"Measured Periods(s) "<<left<<setw(20)<<"Deviation % "<<endl;

	for(i=2.50; i<=4.75; i+=0.25)
	{
		f2=i/gravity;
		f3=sqrt(f2);
		f4=f1 * f3;
		dev=((f4-a[i])-f4)*0.1;
		cout<<left<<setw(10)<<fixed<<setprecision(2)<<i<<setw(20)<<fixed<<setprecision(4)<<f4<<setw(10)<<fixed<<setprecision(4)<<a[i]<<setw(10)<<fixed
			<<setprecision(4)<<dev<<endl;
	}
	system("Pause");
	return 0;
}

[boost lexical cast]

Type double can hold decimal places while int cannot (only whole numbers). You're trying to assign double to int. Which means the decimal places are lost.

Anyways, it's a warning not an error. Declare i as type double. Why were you using an int with floating point values (decimals) in the first place?

[keskiverto]

Those are not 'error'. They are 'warning'. Syntactically ok, but suspicious. In your code they are logically fatal.

The messages should indicate the line, where the issue occurs.

int foo = 42;
foo = 3.14; // first converts 3.14 into an integer (3)and then assigns result to foo
foo += 0.3; // first converts 0.3 into an integer (0) and then adds result to foo 

As general guideline, prefer integral loop counters. For example:

for ( int bar = 10; bar < 20; ++bar ) {
  double gaz = bar * 0.25;
  // use gaz
}

Furthermore: your lines 19 and 28-29:

T array[7];
double odd = 0.42;
std::cin >> array[ odd ]; // error: array indices must be integral 

[DesmondLee]

@boost lexical cast. Thank you for the response. Because i want to show inside the for loop to print out the following :
2.50m : enter value
3.65m : enter value
and... so on till 4.75m.

@keskiverto Thank you for the response. If i wanted to loop with decimal points ? how is the structure should be done.

[boost lexical cast]

DesmondLee wrote:

Because i want to show inside the for loop to print out the following :
2.50m : enter value
3.65m : enter value
and... so on till 4.75m.

Yes, but int cannot store "decimal point" values

[keskiverto]

If i wanted to loop with decimal points ? how is the structure should be done.

Fake it:

#include <iostream>
#include <iomanip>

int main()
{
  std::cout << std::fixed << std::setprecision(2);
  for ( int foo=10; foo < 20; ++foo )	{
    std::cout << foo * 0.25 << " m : \n";
  }
  return 0;
}

[DesmondLee]

@boost lexical cast @keskiverto thanks for the response. I managed to solve it. thanks for the advice.